A conventional in-wheel motor drive assembly is disclosed in Japanese Unexamined Patent Application Publication No. 2009-63043 (PTL 1). The in-wheel motor drive assembly in PTL 1 includes a motor unit, a speed reduction unit, a wheel hub and a reducer lubricating mechanism for supplying lubrication oil to the speed reduction unit. A casing of the motor unit is provided with cooling paths and a heat sink. Cooling water flowing through the cooling paths cools the motor unit.